Okay... a quick Google search on this suggests you might try substituting a double-backslash for the single one just prior to "Microsoft SQL Server" in the following:

Instead of this:

@key = 'Software\Microsoft\Microsoft SQL Server\MSSQLServer\SuperSocketNetLib\Tcp\IpAll',

try this:

@key = 'Software\Microsoft\\Microsoft SQL Server\MSSQLServer\SuperSocketNetLib\Tcp\IpAll',

Here's where I found it:

https://social.msdn.microsoft.com/Forums/sqlserver/en-US/f193114f-6d89-492f-aefc-bef02f99af0c/xpinstanceregread-returning-nulls?forum=transactsql